There are many situations where it is desirable to counteract slipperiness caused by ice, snow, mud, sleet and the like. This can be done, for example, by salting or sanding.
Not least, this applies to airplane runways. Here, urea is used in order to "melt" the icecover and sand with a particular grain size to provide good friction, because airplanes can not tolerate road salt or sand of the wrong grain size. The sand or urea is spread with a special spreading vehicle. The effectiveness of sanding can be considerably increased if the sand is preheated, because the sand then melts solidly to the icecover on the runway and forms a sandpaper-like surface which provides very good friction against airplane wheels during landing and take off.
Sand preheating creates the need for methods and devices to heat the sand. In a currently used system, the sand is stored, continuously heated, in a large silo from which the sand is conveyed to the spreading vehicle and placed in the spreader hopper. The heated sand is conveyed within the spreading vehicle and spread out as desired.
The above described technique suffers from serious disadvantages. In the first place, it requires large investments for the above mentioned sand silo. Secondly, because the entire mass of sand is kept continuously heated, the sand silo represents a waste of energy which also leads to high costs. Thirdly, the technique is not particularly effective because the sand continuously loses heat from the moment it is loaded onto the spreading vehicle. Our measurements show that, in fact, the sand has only a fraction of its warmth left when it reaches the spot where it is to be scattered.